The demands to apply transonic centrifugal compressor have increased in the advanced gas turbine engines. Various techniques are used to increase the aerodynamic performance of the centrifugal compressor. The effects of the inclined leading edges in diffuser vanes of a transonic centrifugal compressor on the flow-field unsteadiness and noise generation are investigated by solving the compressible, three-dimensional, transient Navier–Stokes equations. Diffuser vanes with various inclination angles of the leading edge from shroud-to-hub and hub-to-shroud are numerically modeled. The results show that the hub-to-shroud inclined leading edge improves the compressor performance (2.6%), and the proper inclination angle is effective to increase the stall margin (3.88%). In addition, in this study, the transient pressure variations and radiated noise prediction at the design operating point of the compressor are emphasized. The influences of the inclined leading edges on the pressure waves were captured in time/space domain with different convective velocities. The pressure fluctuation spectra are calculated to investigate the tonal blade passing frequency (BPF) noise, and it is shown that the applied inclination angles in the diffuser blades are effective, not only to improve the aerodynamic performance and stall margin, but also to reduce the BPF noise (7.6 dB sound pressure level reduction). Moreover, it is found that the diffuser vanes with inclination angles could suppress the separation regions and eddy structures inside the passages of the diffuser, which results in reduction of the overall sound pressure level and the broadband noise radiated from the compressor.

In this work, we have proposed and optimized a segmented cladding fiber (SCF) with a large mode area (LMA) consisting of a uniform core and a double cladding. The outer cladding of the SCF consisted of a periodic alternation of high- and low-refractive-index segments, while the inner cladding consisted of a resonant layer of rods surrounded by high-refractive-index rings. The three geometrical parameters chosen as design variables were the (a) doped rod refractive index differences, (b) refractive index differences of rings, and (c) ring thickness. Using the Box–Behnken approach, we selected thirteen different design cases and modeled them numerically using the finite element method (FEM). In order to optimize the features of the proposed fiber, such as the effective mode area (EMA), we applied response surface methodology (RSM). The EMA of the optimal SCF was significantly improved and markedly enlarged to about 706 µm² at a wavelength of 1.550 µm. Different properties of the optimized double-cladding octo-wing SCF (DC-OW-SCF), such as confinement losses in the core mode and the first higher-order mode, were studied. The DC-OW-SCF offers the advantages of feasibility in fabrication using the powder-in-tube (PIT) method and provides the possibility of utilization in compact amplifier devices and high-power fiber lasers.